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Food Microbiology the Role of the Membrane Lipid Composition in The Food Microbiology 78 (2019) 143–154 Contents lists available at ScienceDirect Food Microbiology journal homepage: www.elsevier.com/locate/fm The role of the membrane lipid composition in the oxidative stress tolerance T of different wine yeasts ∗ Jennifer Vázqueza, Karlheinz Grillitschc, Günther Daumb, Albert Masa, Gemma Beltrana, , María Jesús Torijaa a Wine Biotechnology Research Group, Dept Biochemistry and Biotechnology, Faculty of Oenology, University Rovira i Virgili, 43007, Tarragona, Catalonia, Spain b Institute of Biochemistry, Graz University of Technology, 8010, Graz, Austria c Austria Centre of Industrial Biotechnology, 8010, Graz, Austria ARTICLE INFO ABSTRACT Keywords: Oxidative stress is a common stress in yeasts during the stages of the winemaking process in which aerobic Saccharomyces cerevisiae growth occurs, and it can modify the cellular lipid composition. The aim of this study was to evaluate the Non-Saccharomyces oxidative stress tolerance of two non-conventional yeasts (Torulaspora delbrueckii and Metschnikowia pulcherrima) Phospholipids compared to Saccharomyces cerevisiae. Therefore, their resistance against H2O2, the ROS production and the Fatty acids cellular lipid composition were assessed. The results showed that the non-Saccharomyces yeasts used in this study Sterols exhibited higher resistance to H2O2 stress and lower ROS accumulation than Saccharomyces. Regarding the cellular lipid composition, the two non-Saccharomyces species studied here displayed a high percentage of polyunsaturated fatty acids, which resulted in more fluid membranes. This result could indicate that these yeasts have been evolutionarily adapted to have better resistance against the oxidative stress. Furthermore, under external oxidative stress, non-Saccharomyces yeasts were better able to adapt their lipid composition as a defense mechanism by decreasing their percentage of polyunsaturated fatty acids and squalene and increasing their monounsaturated fatty acids. 1. Introduction enzymatic responses, and finally, the adapted cells can resume pro- liferation (Herrero et al., 2008; Jamieson, 1998; Moradas-Ferreira and Our understanding of the response and adaptation of yeasts to ex- Costa, 2000). ternal environmental changes is very important within the biotechno- Biological membranes are primarily made of proteins and phos- logical, pharmaceutical, food and beverage industries. Changes in the pholipids, and they form the first barrier that separates yeast cells and temperature, pH and osmotic pressure, nutrient starvation, ethanol their organelle compartments from their external environment. Fatty toxicity, prolonged anaerobiosis, exposure to chemical preservatives acids (FAs), both free and as part of complex lipids, play a number of and oxidative stress are the primary causes for the decrease in yeast key roles in metabolism. They can be incorporated into phospholipids viability and vitality in industrial processes (Walker and Dijck, 2006; (PLs), which are considered as primary structural elements of biological Gibson et al., 2007). membranes and sphingolipids, or they can serve as an energy reservoir Oxidative stress is the result of an imbalance between the presence in the form of triacylglycerols and steryl esters (Klug and Daum, 2014). of reactive oxygen species (ROS) and the capacity of cells to detoxify Another important and essential group of lipids for maintaining the these reactive intermediates of molecular oxygen, or to repair the re- membrane integrity is the sterols, and ergosterol is the primary sterol in sulting damage. Disturbances in the normal redox state of cells can yeast (Daum et al., 1998; Klug and Daum, 2014). Membrane dysfunc- damage all of their components, including lipids, carbohydrates, pro- tion can be associated with a loss of viability (Avery, 2011). Excessive teins and nucleic acids, and they may even induce programmed cell ROS production can overwhelm the detoxifying mechanism and initiate death (Costa and Moradas-Ferreira, 2001; Gibson et al., 2008; Moradas- changes in the lipid layers composition, resulting in a lipid peroxidation Ferreira et al., 1996). Under normal physiological conditions, yeasts are process, in which unsaturated lipids are converted into polar lipid hy- able to effectively defend themselves against the direct consequences of droperoxides. PLs are particularly susceptible to oxidative damage stress exposure and damage by immediate cellular enzymatic and non- mediated by ROS due to their content of polyunsaturated FAs (PUFAs), ∗ Corresponding author. Dept. Bioquímica i Biotecnologia, Facultat d’Enologia, Universitat Rovira i Virgili, c/ Marcel·lí Domingo no 1, 43007 Tarragona, Spain. E-mail address: [email protected] (G. Beltran). https://doi.org/10.1016/j.fm.2018.10.001 Received 23 November 2017; Received in revised form 16 April 2018; Accepted 5 October 2018 Available online 12 October 2018 0740-0020/ © 2018 Elsevier Ltd. All rights reserved. J. Vázquez et al. Food Microbiology 78 (2019) 143–154 which are more sensitive to peroxidation than monounsaturated FAs deposited in the Spanish Type Culture Collection (CECT) as CECT (MUFAs) (Ayala et al., 2014; Howlett and Avery, 1997). Extensive lipid 13135 and CECT 13131, respectively. peroxidation has been correlated with membrane disintegration and The commercial strains were in active dry yeast form and were re- cell death. However, lethal consequences on membranes are not sys- hydrated according to the manufacturer's instructions. For all experi- tematically observed because yeasts are able to sense and adapt to ments, precultures for biomass propagation were prepared in YPD li- environmental changes by modifying the membrane fluidity and phase quid medium (2% (w/v) glucose, 2% (w/v) peptone and 1% (w/v) transitions and by activating the cellular control of the chemical yeast extract (Panreac, Barcelona, Spain)) and incubated for 24 h at membrane composition. These changes in lipid composition are used by 28 °C with orbital shaking (120 rpm). yeast as a defense mechanism, and they are important for conferring resistance to oxidative stress. (Beney and Gervais, 2001; Los and 2.2. Effect of hydrogen peroxide on yeast growth Murata, 2004). Yeast species, and even different strains of the same species, can Yeast cells were pre-cultured for 24 h and then inoculated into YPD exhibit variations in their membrane lipid composition (Hunter and broth (25 mL) to obtain an initial population of 5 × 105 cells/mL. After Rose, 1972). In fact, yeast membranes are structurally and functionally 6 h (early exponential phase), sublethal oxidative stress was induced in dependent on the growth conditions, e.g., Saccharomyces cerevisiae is each strain by adding 2 mM H2O2 to the yeast culture. Yeast growth was auxotrophic for oleic acid and ergosterol under strict anaerobic condi- followed in both conditions (control and stressed cells) by measuring tions (Walker and Dijck, 2006). Thus, the lipid composition should not the optical density at 600 nm (OD600) every 30 min for 24 h, using a be considered a fixed and static characteristic of a single yeast strain microplate reader (Omega Polarstar, BMG Labtech Gmbh, Ortenberg, (Beltran et al., 2008; Hunter and Rose, 1972; Torija et al., 2003). Germany). Microplate wells were filled with 250 μL of inoculated S. cerevisiae is the primary yeast species involved in wine fermen- media. A control well containing medium without inoculum was used tation (Ribereau-Gayon, 1985; Fleet and Heard, 1993); however, many to determine the background signal. Measurements were taken every other yeast species can participate in different stages of the process 30 min after pre-shaking the microplate for 30 s at 500 rpm. All assays (Beltran et al., 2002). Currently, non-Saccharomyces yeasts are used to were performed in triplicate. produce final products with improved organoleptic characteristics (González-Royo et al., 2015; Jolly et al., 2014). In general, these yeasts 2.3. Resistance to hydrogen peroxide (H2O2) are not able to complete the alcoholic fermentation, several studies have demonstrated that some non-Saccharomyces yeasts used with se- Yeast resistance to H2O2 was assessed using the agar diffusion quential inoculation techniques, can positively contribute to the aroma method (Bauer et al., 1966; Acar, 1980). Approximately 5 × 106 cells profile, sensory complexity and color stability of the resulting product were seeded with glass beads on YPD plates, and 6 mm blank disks were (Fleet, 2008; González-Royo et al., 2015; Mas et al., 2016; Pretorius, impregnated with 10 μL of 30% (v/v), 15% (v/v), 3% (v/v) or 0.3% (v/ 2000). Thus, non-Saccharomyces species can influence the organoleptic v) H2O2 (Perdrogen™, Sigma-Aldrich, MO, USA) and placed on the agar properties of wines, increasing the volatile compounds or secondary surface after drying. One disk impregnated with 10 μL of H2O was used metabolites such as glycerol, aromatic alcohols, esters and acetates as the negative control. After 48 h of incubation at 28 °C, the diameter (Belda et al., 2017; Jolly et al., 2014; Romano et al., 2003). For in- of the inhibition haloes, including the disk, was measured with a ruler stance, Torulaspora delbrueckii has been proposed to reduce the volatile and photographed using a ProtoColHr automatic colony counter (Mi- acidity produced by Saccharomyces (Bely et al., 2008), whereas crobiology International, Frederick, USA). The means of three biolo- Metschnikowia pulcherrima is recommended for the release of some vo- gical
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